Ecological Pyramids and Succession: Understanding Ecosystem Dynamics

In the pyramids of numbers, the lengths of the steps are proportional to the number of individuals of all species in each trophic level per unit area or volume.

Biomass in the lengths of the steps are proportional to the dry weight of all individuals in each trophic level per unit area or volume.

These pyramids best describe the trophic relationships of the ecosystem as they indicate the amount of organic matter that can be eaten at each trophic level, but do not express the amount transferred from one level to another.

Energy in the lengths of the steps are proportional to the energy produced per unit time of all individuals in each trophic level per unit volume or surface.

These pyramids provide a better overall picture of trophic relationships in ecosystems, because they give us an idea of the energy passing from one trophic level to the top through the food chain.

Ecological succession refers to the gradual change that occurs in the community of plants and animals after the emergence of a new substrate or after a strong disturbance, and some communities are being replaced by others over time.

Primary succession

Starts on a new substrate, which has never been colonized significantly by any organism.

This is the case of accumulation of volcanic materials after an eruption, when it is an extension of rock on the surface due to the retreat of glaciers or sedimentary deposits accumulated after a long avenue, dunes, etc.

Secondary succession

Occurs after a strong disturbance that removes the vegetation of an ecosystem but not the soil.

At present, it is easy to see this kind of succession as a result of human disturbance. This is the case of abandoned fields, which will become colonized and initiate a sequence. Other examples include logging, fire, etc.

Succession is a gradual and slow process that affects a number of communities. The changes in vegetation are more apparent and are often used to describe the succession, but there are also changes in animal populations.

The sequence is a sequence of increasingly complex communities called evolutionary series.

Each of the communities that follow and we use to describe the sequence is called a serial stage.

The evolutionary sequence ends when establishing a stable community. The climax community is the culmination of ecological succession and is characterized by stability. It remains stable unless there is a disturbance. If a low-intensity disturbance occurs, the climax community quickly re-establishes itself.

Regression refers to the disturbances experienced by ecosystems that destroy or alter any of the elements that determine the structure of the ecosystem. These disturbances have the effect of facilitating earlier seral stages.

Examples of disturbances include land reclamation to transform crops, logging, grazing, or fire. Thus, upon cessation of the impact, it initiates a secondary succession.